Weather extremes tied to jet stream

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June 25, 2013

Photo: Uncredited, HOPD

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This combination of undated photos released by the Ashland County Sheriff's Office shows, from left, Daniel Brown, Jordie L. Callahan, Jessica L. Hunt, and Dezerah Silsby, who are accused of enslaving a mentally disabled woman and her daughter. A federal magistrate judge on Monday, June 24, 2013 ruled that thereâs enough evidence against them to send the case before a grand jury. Judge Nancy Vecchiarelli made the ruling against Callahan and Hunt in the case and ordered them locked up pending trial. Brown skipped a chance to ask for pretrial release, and Silsby was freed last week to await trial. (AP Photo/Ashland County Sheriffs Office, File) less

This combination of undated photos released by the Ashland County Sheriff's Office shows, from left, Daniel Brown, Jordie L. Callahan, Jessica L. Hunt, and Dezerah Silsby, who are accused of enslaving a ... more

Photo: Uncredited, HOPD

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FILE - In this Sunday, June 23, 2013 file photo, floodwaters inundate homes in Medicine Hat, Alberta. Alberta's municipal affairs minister says 27 communities are under a state of emergency as some areas begin to recover from flooding while others are still bracing for it. Scientists say the erratic jet stream has been responsible for downpours that have led to historic floods in Alberta. (AP Photo/The Canadian Press, Nathan Denette, File) less

FILE - In this Sunday, June 23, 2013 file photo, floodwaters inundate homes in Medicine Hat, Alberta. Alberta's municipal affairs minister says 27 communities are under a state of emergency as some areas begin ... more

Photo: Nathan Denette, SUB

Weather extremes tied to jet stream

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WASHINGTON - Lately, the jet stream isn't playing by the rules. Scientists say that big river of air high above Earth that dictates much of the weather for the Northern Hemisphere has been unusually erratic the past few years.

They blame it for everything from snowstorms in May to the path of Superstorm Sandy.

And last week, it was responsible for downpours that led to historic floods in Alberta, Canada, as well as record-breaking heat in parts of Alaska, experts say. The town of McGrath, Alaska, hit 94. Just a few weeks earlier, the same spot was 15 degrees.

The current heat wave in the Northeast is also linked. "While it's not unusual to have a heat wave in the east in June, it is part of the anomalous jet stream pattern that was responsible for the flooding in Alberta," Rutgers University climate scientist Jennifer Francis said Tuesday.

The polar jet stream affects the Northern Hemisphere. It dips down from Alaska, across the United States or Canada, then across the Atlantic and over Europe and "has everything to do with the weather we experience," Francis said.

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The jet stream usually rushes rapidly from west to east in a mostly straight direction. But lately it's been wobbling and weaving like a drunken driver, wreaking havoc as it goes. The more the jet stream undulates north and south, the more changeable and extreme the weather.

It's a relatively new phenomenon that scientists are still trying to understand. Some say it's related to global warming; others say it's not.

In May, there was upside-down weather: Early California wildfires fueled by heat contrasted with more than a foot of snow in Minnesota. Seattle was the hottest spot in the nation one day, and Maine and Edmonton, Canada, were warmer than Miami and Phoenix.

Here is what federal weather officials call a "spring paradox": The U.S. had both an unusually large area of snow cover in March and April and a near-record low area of snow cover in May. The entire Northern Hemisphere had record snow coverage area in December but the third-lowest snow extent for May.

"I've been doing meteorology for 30 years and the jet stream the last three years has done stuff I've never seen," said Jeff Masters, meteorology director at the private service Weather Underground.